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First published online September 19, 2006
Journal of Experimental Biology 209, 3786-3794 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02447

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Tests of absolute photorefractoriness in four species of cardueline finch that differ in reproductive schedule

Scott A. MacDougall-Shackleton^1,*, Madhusudan Katti² and Thomas P. Hahn³

¹ Departments of Psychology and Biology, University of Western Ontario, London ON, N6A 5C2, Canada
² Department of Biology, California State University, Fresno, USA
³ Section of Neurobiology, Physiology and Behavior, Animal Communication Laboratory, University of California, Davis, USA

View larger version (27K): [in a new window]   Fig. 1. Field data on seasonal changes in length of the left testis (circles) and cloacal protuberance (CP, triangles) in free-living pine siskins, Cassin's finches and gray-crowned rosy-finches breeding at Tioga Pass, California. The line indicates the number of hours of daylight. The hatched bars indicate when most birds of each species were exhibiting feather molt. Testis length was measured in a subset of the birds for which we measured CP. Sample sizes are: pine siskin: 207 (CP), 31 (testis); Cassin's finch: 574 (CP), 82 (testis); gray-crowned rosy-finch: 31 (CP), 6 testis.

View larger version (24K): [in a new window]   Fig. 2. Field data on seasonal changes in length of the left testis (circles) and cloacal protuberance (CP, triangles) in free-living red crossbills captured in the vicinity of Washington State. The hatched bars indicate when most birds were exhibiting feather molt. Testis length and CP were measured in the same birds. Sample size is 308 birds.

View larger version (13K): [in a new window]   Fig. 3. Comparison of testis length of pine siskins, Cassin's finches and gray-crowned rosy finches across two times in the breeding season when day length varies between 14.0 and 14.5 h light (May: 8-26 May; July: 19 July-4 Aug) at Tioga Pass, California. Bars indicate mean ± s.e.m. For P values, see text. Asterisks denote significant differences between times. Numbers within bars indicate sample size.

View larger version (17K): [in a new window]   Fig. 4. Testis size of birds maintained on short days or transferred to 24 h light in Experiment 1. Bars indicate mean ± s.e.m. For P values, see text. Asterisks denote significant differences; NS, no significant difference. Sample sizes are red crossbill: 4, 4; pine siskin: 5, 5; Cassin's finch: 4, 4; gray-crowned rosy-finch: 3, 3.

View larger version (11K): [in a new window]   Fig. 5. Circulating levels of luteinizing hormone in birds exposed to short days (triangles) or 24 h light (open circles) 4 days prior to the change in photoperiod (d -4) and 3 and 10 days following it. Values are means ± s.e.m. Sample sizes as in Fig. 4.

View larger version (20K): [in a new window]   Fig. 6. Relative testis size of birds maintained on short days (SD) or transferred to 24 h light (24L) in Experiment 2. Bars indicate mean ± s.e.m. Broken line indicates 100%, or no change in testis length. Sample sizes are 4 birds per group for all three species.

View larger version (11K): [in a new window]   Fig. 7. Distribution of criteria 1 and 2 for absolute photorefractoriness among four species of cardueline finches. Criterion 1 indicates whether or not the species spontaneously regresses gonads on constant long days [data are taken from: 1(Hahn, 1995); 2(Hahn et al., 2004); 3T.P.H., unpublished data (based on molt and cloacal protuberance)]. Criterion 2 indicates whether or not the species responds to very long days when putatively photorefractory (data from this study). Phylogeny based on Marten and Johnson, and others (Marten and Johnson, 1986; Badyaev, 1997; Arnaiz-Villena et al., 2001).